Vented Atic Roof Assembly

Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction.

Vented atic roof assembly.

Ci to be installed in multiple layers to limit insulation by pass from gapping of insulation. Sc historically typical construction of homes in canada and the us have vented attics between the ceiling of the interior space and the roof. The quest for greater energy efficiency in buildings has led to increasing interest and need for insulation improvements in hvac equipment more airtight construction new materials and assemblies. Roof sheathing to be air sealed.

The total insulation r value for the assembly will be an r 39 r 20 r 19. In a roof attic assembly the builder has two choices. The thermal boundary can be at the ceiling plane leaving the attic space above uninsulated and vented or the thermal boundary can be located at the roof line creating a sealed insulated conditioned or semi conditioned attic space. R value of ccspf to be 40 of total assembly.

To be placed on the underside and in direct contact with the roof sheathing. The building envelope is tight enough to prevent warm moist air from escaping from the building interior into the roof assembly. If less analysis is required. Based on table r806 4 r 20 rigid board insulation will be required to be placed on top of the roof deck to keep the condensing surface temperature at or above 45 f.

Some manufacturers don t warranty or offer only a limited warranty when their products are used over an unvented roof assembly. This can reduce their service life by roughly 10. These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck. An unvented assembly can perform well but it s important to get the details right to avoid sheathing rot.

Acceptable if above is not feasible. Senior engineer manager at icynene john broniek makes the case for the unvented attic assembly and why insulating the underside of the roof makes sense. Un ven ted roof ˌənˈven t əd ro of an unvented roof assembly is constructed without any ventilation and is fully sealed on all sides and filled with insulation. Shingles that are installed on unvented roof assemblies operate at slightly higher temperatures roughly 2 f to 3 f warmer than shingles on vented assemblies.

Closed cell spray polyurethane foam ccspf at bottom of roof sheathing.